A foreign aircraft was forced to land Thursday by two Indonesian Air Force (TNI-AU) fighter jets at the Soewondo Airbase in Medan, North Sumatra, after the plane entered Indonesian airspace without authorisation.

The red civilian aircraft, with registration number N54JX, was intercepted by two TNI-AU F-16 jets at 12:44 p.m. Armed Air Force personnel, assisted by sniffer dogs, examined the plane after landing at Soewondo Airbase.

They did not find anything suspicious inside the plane, only three jerry cans of fuel and a bicycle.

As of Thursday afternoon, the plane was being tightly guarded by TNI-AU personnel, as the pilot, identified as Heinz Pieter, was being questioned at the airbase.

National Defense Sektor III commander Air Marshal Sungkono said the Air Force fighter jets were conducting an operation over Sumatra, when suddenly an unauthorised foreign plane was detected on their radars.

Sungkono added that the two F-16s immediately intercepted the plane.

“The foreign aircraft was intercepted 80 nautical miles west of Meulaboh, Aceh. The plane was then forced to land at the Soewondo Airbase,” Sungkono said at the airbase in Medan on Thursday.

He added that the authorities were still questioning the pilot. Sungkono said that based on initial questioning, the plane was en route from Colombo in Sri Lanka to Singapore. He added that the pilot had claimed he was unaware he had entered Indonesia’s airspace.

“Based on his statement, it seems the pilot did not know the country’s territory,” Sungkono said, adding that Pieter was a retired commercial airline pilot from Switzerland.

Sungkono said his command had not discovered any indication of threat from the foreign aircraft.

“As yet, there seems to be no threat to our territorial sovereignty. He [Pieter] appears to be guilty only of not having a permit, which he should have had before entering our territorial airspace. But we are still investigating the incident,” he said, adding that the Swearingan SX-300 civilian plane was personally owned by the pilot.

Pieter, 65, has told authorities at the airbase that he was flying his private plane to travel solo around the world and that he was not aware that he had entered Indonesian airspace.